Process for producing synthetic rubbers containing tackifiers and softeners and product thereof



Patented Sept. 23, 1952 RUBBERS GONTAINING AND THEREOF TACKIFIERS SOFTENERS AND PR 0 D U C '1 Harry Burrell, Milburn, and Robert H. Barth, Ridgewood, N. J assignors to Heyden Chemical Corporation, New York, N. .Y., a corporation of Delaware No Drawing. Original application November 13,

1944, Serial No. 563,310. Divided and this application July 21, 1850, Serial No. 175,292

8 Claims.

7 1 Our invention relates particularly to a process of producing compositions containing new and useful chemical compounds-together with"syn-' thetic rubbers, such as 'copolymers of diolefins and styrene and copolymers of diolefins and acrylonitrile. In one of its more specific aspects it relates to acetals of partial esters of certainpolyhydric alcohols, such as the diabietic acid ester of pentaerythritol butyral, which are especially advantageous tackifiers and tack-imparting or tackifying softeners for synthetic rubbers. This application is a division of our application upon Resin-Acid Ester-Acetals of Polyhydric Alcohols, Ser. No. 563,310, filed November 13, 1944, which is a continuation in part of our prior copending application Ser. No. 525,592, filed March 8, 1944, which issued as Patent No. 2,446,257.

Synthetic rubbers, such as copolymers of butadiene and styrene (Buna-S or GR-S) and copolymers of butadiene and acrylonitrile (Buna-N, Hycar-OR, or GR-A) and the like, differ from natural rubber in many respects, especially in the quantities and types of compounding ingredients which must be incorporated therewith and in the compounding procedures which must beused to produce automobile tires and other useful articles therefrom. "Carbon black, for example, must be incorporated in greater quantities insynthetic rubber of the GR-S type than in natural rubber to produce automobile tires, and special grades of carbon black must be used for the purpose. Different vulcanizing agents, softening agents and the like are also used. Softeners are generally used with both natural and synthetic rubber but, when used with these synthetic rubbers, greater proportions are required and theeffects produced they must be used in such quantities as to destroy at least partially what little inherent tackiness is possessed by the synthetic rubber. As a consequence, the industry has long sought softeners that improve the tackiness or coherence of synthetic rubbers and permit it tov be milled and treated in much the same manner as natural rubber or substances which, when added to con-- 2 vention-al synthetic rubber compositions, improve the tackiness of the resulting compositions, especially during milling.

It is a principal object of the present invention to provide a tackifier for synthetic rubber compositions, such as those produced from copolymers of butadiene and styrene and copoly mers of butadiene and acrylonitrile.

It is a further object to provide a tackifier for such synthetic rubber compositions that will retain a considerable portion of its efiectiveness after vulcanizationof the compositions.

A further object of the invention is to provide a material which may be used as both a softening,

and tackifying ingredient for compositions comprising such synthetic rubbers.

Other objects and advantages of the invention, some of which are referred to more specifically hereinaftenwill be apparent to those skilled in the art to which the invention pertains. We have discovered that the foregoing objects are realized to a remarkable degree by the use of certain new and novel compounds which we described in our copending application Sen-No. 525,592, filed March 8, 1944, which issued as Patent No. 2,446,257. These compounds are exemplified by pentaerythritol diabietate butyral, which may possibly be representable structurally as: I

AbietylO-HzG CHL -O CHr-O pared generally by partial esterification of glycerol, pentaerythritol, a polypentaerythritol, or mixtures thereof, with abietic acid or a similar acid or'a material, such as tall oil, containing a substantial proportion of such acids. This esterification may be effected by heating the two materials in the presence of a catalyst but it normally proceeds sufiiciently rapidly without a catalyst in the temperature range from approximately 180 to approximately 300 C. or somewhat higher. Catalysts which may be used, if desired, are

sulfuric acid, p-toluenesulfonic acid, resinates and naphthenates of lithium, calcium, strontium, barium, zinc and cadmium and other soluble salts of these metals, as described in Burrell Patent No. 2,360,394, and the like. When pentaerythritol esters are being prepared, care should be exercised not to overheat the pentaerythritol before the esterification has proceeded to a substantial extent, since overheating may result in the de composition of the pentaerythritol with the formation of dark-colored products and undesirable byproducts. After the partial ester has been formed it is then reacted with an aldehyde to produce an acetal.

The reaction of the partial ester with the aldehyde may be conducted by heating the two materials together in the presence of an acid catalyst, such as oxalic acid, hydrochloric acid, sulfuric acid or the like. It is desirable to add an inert solvent such as toluene or a saturated aliphatic hydrocarbon or petroleum fraction to prevent foaming and to aid in removing the water formed in the reaction. As the acetalization proceeds, the reaction temperature may be raised. It is generally desirable to conduct the acetalization in an apparatus provided with a reflux condenser, separator or trap, and a return line, and to effect the heating in the presence of toluene or other solvent which is immiscible with water but which formsjan azeotrope with water. By using such an apparatus and such a solvent, the reactants can be heatedunder gentle reflux and the temperature can be more readily controlled. In operating in this manner, the condensed reflux liquid is collected in the separator or trap, the water is separated therefrom periodically, and the toluene is returned to the reaction mass. At the end of the acetalization the solvent can be removed by volatilization, preferably at reduced pressure, that is, by vacuum distillation.

Instead of preparing the partial ester by heating the acid and polyhydric alcohol together in the desired stoichiometric proportions a complete ester may be used as the starting material. The complete ester may be alcoholized with glycerol, pentaerythritol or a polypentaerythritol, in the presence of catalysts, if desired, to form the partial ester. Thus pentaerythritol tetra-abietate may be reacted with pentaerythritol to produce pentaerythritol diabietate in the presence of catalysts such as are disclosed in Burrell Patent No. 2,360,394. 1

Although, in the preparation of compounds for use as tackifiers from pentaerythritol, in accordance with the process of the present invention, it is generally desirable to have two of the hydroxyl radicals of pentaerythritol esterified by abietic acid or its equivalent and the remaining two acetalized by the aldehyde, these proportions may be varied considerably. With pentaerythritol, satisfactory products may be obtained from the reaction of one molecular equivalent to three molecular equivalents of abietic acid and the acetalization of the remaining hydroxyl groups. With dipentaerythritol, which contains six hydroxyl groups per molecule, from one to five of the hydroxyl groups may be esterified with abietic acid and the remaining hydroxyl groups may be acetalized. When glycerol is used as the starting material, either one or two hydroxyl groups may be acetalized.

The composition of the products which are formed has not been definitely established but obviously they are somewhat more complex than indicated by the probable structure of pentaerythritol diabietate butyral as given hereinabove. The products may be pure compounds or mixtures of pure compounds, in which there may be crosslinkages between the original polyhydric alcohol nuclei through the acetal group. A possible compound, for example, which has such cross-link ages and also has the same empirical composition as pentaerythritol diabietate butyral, is:

which is a dipentaerythritol tetra-abietate dibutyral.

The order of the esterification and acetalization may be reversed but esterification prior to acetalization is recommended and preferred because of its simplicity.

Instead of using pure abietic or sylvic acid in the production of the tackifiers or tackifying softeners of the present invention, rosin of various grades or degrees of purity may be used. Pure abietic acid has an acid number of 162, whereas grade B wood rosin, which may also be used as a starting material, may have an acid number as low as 110. Of course, compensation for these differences should be made, for example, by using these acid numbers in computing the quantities of the polyhydric alcohol to be used for esterification. Tall oil or tallol, which is rich in resin acids, containing as much as 40% by weight of these acids which include substantial amounts of Steeles abietic acid and d-pimaric acid, may also be used to replace abietic acid, either partially or completely. Other acids of the type of abietic acid which may be used for partial or complete replacement of abietic acid are levopimaric acid, d-pimaric acid and Palkin acids.

Glycerol, pentaerythritol, polypentaerythritols and mixtures thereof are the preferred polyhydric alcohols for use in producing the compounds of the invention. Dipentaerythritol and tripentaerythritol are two of the polypentaerythritols which have been definitely isolated and identified. Pleopentaerythritol, one of the products that can be isolated from the condensation of formaldehydeand acetaldehyde in the presence of an alkali, and which has a melting point of 230 to 240 C. and a hydroxyl content of 33%, possesses some of the atrtibutes of a pure compound, but is a mixture of dipentaerythritol and tripentaerythritol with other hydroxylated products. Tetrapentaerythritol and higher polypenttaerythritols have been postulated at the present ime.

The polyhydric alcohols which may be used for the production of tackifying compounds in accordance with the invention are relatively restricted. Thus, ethylene glycol, propylene glycol, diethylene glycol and the like do not produce compounds which exhibit to any substantal extent the desirable properties possessed by acetals of abietic esters of glycerol, pentaerythritol and polypentaerythritols. The efiect of using a diethylene glycol diabietate butyral in a butadienestyrene copolymer is illustrated in the preparatf'iftlll entitled Comparison Composition 1 herein a er.

The aldehydes which may be used in the production of the acetals of abietic acid esters of polyhydric alcohols in accordance with the process of the invention are formaldehyde, acetaldehyde, propionaldehyde, butyraldehyde and other aliphatic aldehydes having up to and including eight carbon atoms in the molecule. Aromatic aldehydes such as benzaldehyde may also be used. Instead of using an aldehyde itself, the starting material may. be a partially acetalized polyhydric alcohol, for example, a mixture of formals of pentaerythritol and polypentaerythritols such as is formed as a byproduct in the production of pentaerythritol and polypentaerythritols by the condensation of formaldehyde and acetaldehyde in the presence of an alkaline catalyst.

The preferred products of the invention are those in which all the hydroxyl groups of the polyhydric alcohol have been combined, that is,

some with abietic acid or its equivalents and some with an aldehyde. However, compounds with free hydroxyl groups or mixtures containing some compounds having uncombined hydroxyl groups, as well as compounds of this type in which one or more of the hydroxyl groups has been esterified by acetic acid or other aliphatic or aromatic acids, may also be used.

Although the acetals of abietic esters of polyhydric alcohols which are described herein are especially adapted for use with synthetic rubbers of the types represented by copolymers of butadiene and styrene (GR-S) and copolymers of butadiene and acrylonitrile (GR-A), they may be used generally with all synthetic rubbers which are copolymers of a 1,3-butadiene hydrocarbon and another unsaturated compound which contains a CH2=C: group and is copolymerizable therewith.

In the following examples, which are not to be construed as limitative of the invention, are described methods of preparing suitable compounds for use as tackifying agents in accordance with the process of the invention. Following these examples are illustrated typical compositions containing synthetic rubber and these tackifying agents and results of vulcanizing or curing tests of such compositions.

Example 1.--Pentaerythritol diabietate butyral A mixture of 2000 parts of rosin (acid number=162) and 417 parts of technical pentaerythritol (hydroxyl value=46.5%; combining weight=36), was heated for two hours at 280 C. under an atmosphere of carbon dioxide. The mixture was then cooled to approximately 80 C. and 236 parts of butyraldehyde were slowly added. During the slow addition of the butyraldehyde, concentrated hydrochloric acid was added dropwise until parts had been added. Then 250 parts of toluene were added and the mixture heated gently under reflux with progressively increasing temperature, in an apparatus in which the reflux condenser was connected to a trap in which the condensed toluene-water azeotrope collected. The water was separated and removed periodically from the trap and the toluene was returned to the reaction mixture. After no further substantial quantity of water collected in the trap, the toluene was removed from the reaction mass by vacuum distillation.

The product was a heavy oil which solidified on cooling to a hard, brown, glassy and brittle substance having a low softening point C. or higher).

Methods of compounding this product with copolymers of butadiene and styrene (see Composition 1 hereinafter) and butadiene and acrylonitrile (see Composition 2 hereinafter) are de- 6 scribed hereinafter and the effects produced in such copolymers are tabulated in Table 1.

Example 2.Pentaerythritol diabzetate butyral A mixture of 900 parts of resinous pentaerythritoldiabietate and parts of butyraldehyde was heated to G. Then 1.5 parts of oxalic acid were added and the mixture was heated at approximately 100 C. for two hours. Most of the water formed in the reaction was removed during this period. To the reaction mass were then added 100 parts of toluene and the mixture was heated under gentle reflux in an apparatus similar to that described inExample 1, in such manner that the water which distilled over as an azeotrope with toluene was separated from the toluene and periodically removed. After about five hours of heating, during which time the temperature rose from 100 to 150 C., the toluene was removed together with the remaining water.

The resulting product. was substantially identical with that formed in Example 1.

Example 3.Pentaerythritol diabz'etate benzol Pentaerythritol diabietate benzal, the benzal of the partial abietic acid ester of pentaerythritol, was prepared by reacting pentaerythritol with sumcient wood rosin to esterify approximately one-half of the hydroxyl groups of the pentaerythritol by abietic acid. The mixture of rosin and pentaerythritol was heated slowly to 280 C. in 3 hours. An atmosphere of carbon dioxide gas was maintained over the batch to prevent the formation of oxidation products that darken the color.

The resulting diabietate of pentaerythritol was then reacted with sufficient benzaldehyde to acetalize the remaining hydroxyl groups of the pentaerythritol by heating the mixture together with a small proportion of hydrochloric acid under gentle reflux for 1 hour. A small amount of toluene was added prior to heating the reaction mixture in order to suppress foaming. The unreacted benzaldehyde, water and toluene were then distilled from the batch by heating at 200 C. for 30 minutes.

The product was a hard, brown-colored, homogeneous friable solid that retained a slight odor of benzaldehyde. The yield was 88% of the theoretical.

The effects produced by using this product in the compounding of a synthetic rubber consisting of a butadiene-styrene copolymer (Composition 3) are tabulated in Table 2 hereinafter.

Example 4.Glycerol abietate butyml Four equivalents (124 rams) of glycerol were heated with 2 equivalents (690 grams) of wood resin at 250 C. for 2 hours in a flask equipped with a mechanical stirrer, thermometer and a steam-jacketed condenser. The mixture was thereafter cooled to C, a water-jacketed condenser substituted for the steam-jacketed condenser, and 3 equivalents (108 grams) of butyraldehyde were added together with a small proportion (25 grams) of concentrated hydrochloric acid. The mixture was heated under gentle reflux for 2 hours, during which time the temperature of the batch increased from 83 to 96 C. The water of reaction, unreacted butyraldehyde and unreacted glycerol were then removed by vacuum distillation at a pressure of 5 mm, during which the temperature rose to C.

The product was a dark brown-colored viscous 7 liquid that retained a slight odor of butyraldehyde.

The efiects produced by incorporating this product in a butadiene-styrene copolymer (Composition. l) are tabulated in Table 2 hereinafter.

Comparison Example 1.Diethylene glycol diabietate butyral The diabietate of diethylene glycol was prepared by heating together at 220 C. for 3 hours a mixture consisting of 318 grams of diethylene glycol and 1035 grams of wood rosin, color N (acid value=l62).

The diabietate of diethylene glycol was then heated under reflux for 4 hours with a stoichiometric excess of butyraldehyde in the presence of 20 grams of concentrated hydrochloric acid. The unreacted butyraldehyde and water of reaction were then distilled off at a presure of 5 to mm.

The product was a viscous brown-colored liquid having a slight odor of butyraldehyde.

Results obtained on compounding this product with a butadiene-styrene copolymer (Comparison composition 1) are tabulated hereinafter in Table 2.

formals of pentaerythritol and polypentaerythritols that was obtained as a byproduct in the manufacture of pentaerythritol by the condensation of formaldehyde and acetaldehyde in the presence of an alkaline catalyst, which was recovered in accordance with the process described in the application for patent Ser. No; 484,242, filed April 23, 19:3, by Karl A. Fisher and Harry Burrell, and which is therein referred to as B-liquor.

To 495 parts by weight of the above mixture of formals was added 2000 parts of wood rosin, grade N, which is sunicient to esterify approximately one-half of the hydroxyl equivalent of the mixture, and the mixture was heated for 3 hours at 280 C. The resulting product was then cooled to approximately 100 C. and 240 parts by weight of butyraldehyde and 5 parts by weight I of concentrated hydrochloric acid HCI) were added. This mixture was then heated under total reflux for 4 hours. The unreacted butyraldehyde and volatile products were removed by distillation at a pressure of several millimeters.

The product was a light amber-colored solid that was tacky and very cohesive.

Incorporation of the product into butadienestyrene copolymers (Composition 5) and the effects produced therein are tabulated in Table 3 hereinafter.

Example 6.Quarter-abletates of mixed formals and butymls of pentaerythrz'tol and polypenteerythritols 8 Example 7.TalZ-oil esters of mixed formals and butymls of pentaerythritol and polypentaerythritols A mixture of partial formals of pentaerythritol and polypentaerythritols such as was used in Example 5 was esterified with clay-treated tall oil (Trostol, a tall oil marketed by Champion Fibre and Paper Co.) that had the following characteristics:

Acid number 163 Resin acids per cent 45.2 Fatty acids do 47.3 Combining weight 345 Sterols, etc per cent 7.0 Moisture do 0.6 Ash do 0.35

One hundred seventy (170) parts by weight of the tall oil were mixed with 748 parts by weight of the mixture of partial formals and heated for 2 hours at 275 C. The product was then reacted with butyraldehyde in excess and recovered as in Example 5.

The product consisted of a dark brown-colored viscous liquid.

The effects produced on incorporating the product into a butadiene-styrene copolymer (Composition 7) are tabulated in Table 3.

In general, pentaerythritol diabietate butyral and related compounds, to which the present specification is directed, are hard, brittle resinous solids which are generally brown in color, have low melting points or ranges, and low acid numbers (approximately 10 or less). They are soluble in various solvents, such as acetone, xylene, benzene and toluene, and are compatible with linseed oil, petroleum oils, natural and synthetic rubbers and with natural and synthetic resins. They are also compatible with rosin and waxes and may be used as ingredients in the production of sealing wax and similar compositions.

When added to synthetic rubber compositions comprising such materials as butadiene-acrylonitrile and butadiene-styrene copolymers in amounts up to approximately 2 to 3% by weight of the copolymer, pentaerythritol diabietate butyral and related compounds greatly improve the milling characteristics. In amounts up to approximately 40% by weight of the copolymer, the uncured synthetic rubber compositions possess considerable tack and show long fingers but the cured rubber will not be sticky and will retam good nerve. With greater amounts, in excess of approximately 40% by weight of the copolymer, pronounced tack, softening and plasti claim; are produced and this tack is retained to a considerable extent after curing or vulcaniaation. These effects are produced without other significant changes in the properties of the rubber compositions, but the curing time of the composition is generally retarded slightly.

In using pentaerythritol diabietate butyral and the related tackifying compounds of the present invention in the production of synthetic rubber compositions, conventional compounding procedures may be adopted. Except for providing for slightly increased curing periods, no substantial changes in compounding or curing procedures are required. Generally it is desirable to incorporate the tackifying compound directly with the copolymer on the rubber mill by breaking down the copolymer at a suitable temperature, for example, 33 C. F), and adding the tackifying compound thereto. The additional compounding ingredients may subsequently be incorporated or blended therein. The temperature at which the milling is most advantageously conducted will be dependent upon the amount of tackifying compound that is added. In some cases it may be necessary to cool or chill the rolls below normal operating temperature because of the softness of the composition.

corporated, the uncured composition had excellent tack, and the vulcanized product was free from tack. p

Identical compositions prepared by the incorporation of dibutyl phthalate instead of the pentaerythritol diabietate butyral were also tested for comparison.

The results are as follows:

TABLE 1 Modulus, pounds per Ultimate 353 square inch, atper- Tensile gg 53 Product Cure cent Emngatmn Strength Elongaeter a t 52F23 tion, Hard- 300 F. 300% 500% 700% inch percent ness Butadiene-Styrene 1, 330 870 55 RubberrPentaerythritol l, 570 780 Diabietate Butyral (Composition 1) 1, 640 690 60 Butadiene-Acrylonitrile 15 2, 205 860 Rubber-Pentaerythritol 30 2, 700 750 Diabietate Butyral (Composition 2) 60 3, 670 70 Butadiene-Styrene 15 825 480 50 Rubber-Dibutyl. 30 1, 030 460 56 Phthalate 60 l, 440 55 Butadiene-Acrylonitrile- 15 770 940 46 Rubber-Dibutyl 30 1, 990 50 Phthalate 6O 1, 725 920 55 Preferred methods of compounding the tack- Composition 3 ifymg compounds of the invention and typical synthetic rubber compositions containing such A butadlene-styrene copolymer RFS) c m- One hundred (100) parts by weight of a butadiene-styrene copolymer (GR-S) rubber were rolled on a rubber mill at a temperature of 38 C. (100 F.). While being thus subjected to break down, 25 parts by weight of the pentaerythritol diabietate butyral tackifying compound prepared as described in Example 1 were added in small proportions during the milling. The composition milled easily and became tacky during the mixing. After the tackifying compound had been thoroughly distributed and incorporated, a mixture of 50 parts by weight of channel black and 5 parts by weight of zinc oxide, 1.25 parts by weight of sulfur powder (flowers of sulfur) and 1.25 parts by weight of a commercial accelerator (Altax) were added during continued milling. The composition was then removed from the rolls and was subjected to vulcanization tests.

The product is sticky and tacky during milling but is free from tack after vulcanization. Physical characteristics of vulcanized products prepared from this composition are tabulated in Table 1 hereinafter.

Composition 2 The foregoing example was repeated but, instead of using a butadiene-styrene copolymer, the composition Wasprepared from a butadieneacrylonitrile copolymer, (GR-A) sold under the trade-name I-Iycar OR-15. The tackifier was readily incorporated in this manner and the product before curing had excellent tack but was free from tack after vulcanization.

Physical characteristics of the vulcanized products prepared from this composition are tabulated in Table 1 hereinafter.

Curing tests of Compositions 1 and 2 Portions of the synthetic rubber compositions prepared in Compositions 1 and 2 above were cured at a temperature of 300 F. for periods of 15, 30 and 60 minutes, respectively, and the physical properties of the products were determined. In both cases the tackifier was very readily inposition was prepared from the following:

100 parts by weight of butadiene-styrene copolymer (GR-S) 25 parts by weight of pentaerythritol diabietate benzal (Example 3) 50 parts by weight of channel black 5 parts by weight of zinc oxide 2 parts by weight of sulfur r I 2 parts by weight of accelerator (Altax The milling and incorporation was effected as described in Composition lhereinabove. The

curing and physical characteristics of vulcanized products prepared from this composition are tabulated in Table 2 hereinafter.

Composition 4 A composition was prepared exactly as Com position 3 except that the glycerol abietate butyral of Example 4 was used instead of pentae rythritol diabietate benzal.

Physical characteristics of vulcanized products prepared from this composition are tabulated in Table 2 hereinafter.

Comparison composition 1 A composition was prepared exactly as Composition 3 except that the diethylene glycol diabietate butyral of Comparison Example 1 was substituted for pentaerythritol diabietate :benzal, Weight for weight.

Physical properties of cured products prepared from this composition are tabulated in Table 2 hereinafter.

Curing tests of Compositions 3 and 4 an Comparison composition 1 diabietate butyral, the tackifying ingredient was incorporated very readily by the procedure described and all the compositions possessed excellent tack during milling except Comparison composition 1. Diethylene glycol diabietate butyral is quite unsatisfactory for use as a tackifying ingredient for synthetic rubber in accordance with the process of the present invention.

12 respects the composition was prepared as described in Example 3.

Curing tests of Compositions 5, 6 and 7 The results of curing tests of the three foregoing compositions, which were conducted in the same manner as the curing tests of Compositions 1 and 2, are tabulated in Table 3. For compari- TABLE 3 Modulus, pounds per Ultimate square inch, at per- Tensile g 33;;

Product Compounded with GR-S Cure Gent Elongation ig Elongeeter n t 1%,, sq tion, Hard- 300 F. 300% 500% 700% inch percent ness Penteerythrltol 15 s70 55 Diabietate Butyral. 30 780 55 (Composition l) 60 590 60 Half-Abietetes L.-. 15 910 65 IE-Liquor" Butyral 30 750 70 (Composition 60 560 70 Quarter-Abietates 0 '15 620 60 B-Liqu'or Bntyrals 30 550 60 (Composition 6) 60 550 60 Tell-Oil Esters of 530 50 B-Liquor Butyrals 490 55 (Composition '7) 60 B40 In all compositions, including Comparison composition 1, no tackiness or only slight tackison, the results obtained in such tests with Composition 1 are included TABLE 2 Modulus, pounds per Ultimate square inch, at per- Tensile l shore cent Elongation Stren th mate iDumm' Products Compounded with G-R-S Cutre poungds Eltongafieter1 a ion at per sq. 1 300 F. 300% 500% 700% inch percent ness Pentaerythritol 15 335 670 950 l, 330 870 55 Diabletate ButyraL I 30 490 890 l, 380 1, 570 780 '55 (Composition 1) 60 680 l, 140 l, 640 690 60 15 500 880 1, 400 1, 875 800 55 s a as as 1, 7 590 so 15 545 l, 000 1, 530 l, 780 770 5 5 Butyral 30 800 1, 340 1, 600 530 60 (Composition 4) 60 510 1, 000 1, 4o0 l, 810 775 Diethylene GlycoL 15 800 l, 520 l, 530 500 Dlabietate Butyral. l. 30 706 1, 360 1, 530 495 55 (Comparison Composition 1) 745 l, 370 1, 430 500 55 ness remained in the respective products after 45 In all the above compositions (l, 5, 6 and 7) the Composition 5 A composition was prepared exactly as Composition 3 except that the half-abietates of mixed formals and butyrals of pentaerythritol and polypentaerythritols of Example 5 were used, weight for weight, as the tackifying ingredient, in place of pentaerythritol diabietate benzal.

Composition 6 The quarter-abietates of mixed formals and butyrals of pentaerythritol and polypentaerythritols of Example 6 were substituted weight for weight for the tackifying ingredient used in Composition 3 and in other respects the composition was prepared as described in Example 3.

Composition 7 The tall-oil esters of mixed formals and butyrals of pentaerythritol and polypentaerythritols whose preparation is described in Example 7 were substituted weight for weight for the tackifying ingredient used in Composition 3 and in other tackifying ingredient was incorporated very readily by the procedure described and all the compositions possessed excellent tack during milling. No tackiness or only slight tackiness remained in the respective products after curing at 300 F. for the specified intervals, although the sample of Composition 7 that was cured for 60 minutes was slightly but definitely tacky. lncreasing the time of curing appears to favor development of after-curing tackiness in synthetic rubber composition comprising the tackifiers of the invention.

In all the above compositions (1, 5, 6 and 7) the curing time was slightly retarded by the addition of the tackifiers, being least retarded by the tall-oil esters of mixed formals and butyrals of pentaerythritol and polypentaerythri'tols (Composition 7).

Although the foregoing description comprises preferred embodiments of the invention, it is to be understood that the invention is not limited thereto and that modifications and variations may be made therein without departing substantially from the principles or scope of the invention. 7

We claim:

1. A composition comprising initially a synthetic rubber prepared by the copolymerization of a 1,3-butadiene hydrocarbon and a member selected from the'group consisting of styrene and acrylonitrile and, as, a tack-imparting softener therefor, an ester-acetal of a polyhydric alcohol selected from the group consisting of glycerol, pentaerythritol and polypentaerythritols, in which at least one but not all of the hydroxyl groups of the alcohol has been esterified by a resin acid selected from the group consisting of d-pimaric acid, levopimaric, abietic acids and Palkin acids, and the remaining hydroxyl groups have been acetalized in pairs by an aldehyde selected from the group consisting of aliphatic aldehydes having not more than 8 carbon atoms in the molecule and benzaldehyde.

2. A composition comprising initially a synthetic rubber prepared by the copolymerization' of a 1,3-butadiene hydrocarbon and a member selected from the group consisting of styrene and acrylonitrile and, as a tack-imparting softener therefor, a composition comprising the reaction product of an aldehyde selected from the group consisting of aliphatic aldehydes having not more than 8 carbon atoms in the molecule and benzaldehyde, with an abietic acid ester of a polyhy dric alcohol selected from the group consisting of glycerol, pentaerythritol and polypentaerythritols.

3. A composition comprisin initially a copolymer of 1,3-butadiene and styrene and, as a tackimparting softener therefor, an ester-aceta1 of a polyhydric alcohol selected from the group consisting of glycerol, pentaerythritol and polypenta erythritols, in which at least one but not all of the hydroxyl groups of the alcohol has been esterified by a resin acid selected from the group consisting of d-pimaric acid, levopimaric acid, abietic acids and Palkin acids, and other hydroxyl groups have been acetalized in pairs by an aldehyde selected from the group consisting of aliphatic aldehydes having not more than 8 carbon atoms in the molecule and benzaldehyde.

4. A composition which comprises a synthetic rubber prepared by the copolymerization of a 1,3-hutadiene hydrocarbon and a member selected from the group consisting of styrene and acrylonitrile and incorporated therewith as a tack-imparting softener, an ester-acetal of a polyhydric alcohol selected from the group consisting of glycerol, pentaerythritol and polypentaerythritols, in which at least one but not all of the hydroxyl groups of the alcohol has been esterified by a resin acid selected from the group consisting of a d-pimaric acid, levopimaric, abietic acids and Palkin acids, and the remaining hydroxyl groups have been acetalized in pairs by an aldehyde selected from the group consisting of aliphatic aldehydes having not more than 8 carbon atoms in the molecule and benzaldehyde.

5. A composition which comprises a synthetic rubber prepared by the copolymerization of a 1,3-butadiene hydrocarbon and a member se lected from the group consisting of styrene and acrylonitrile and incorporated therewith as a 6 A composition which comprises a copolymer" of 1,3-butadiene and styrene and incorporated therewith as a tack-imparting softener, an esteracetal of a polyhydric alcohol selected from the group consisting of glycerol, pentaerythritol and polypentaerythritols, in which at least one but not all of the hydroxyl groups of the alcohol has been esterified by a resin acid selected from the group consisting of d-pimaric acid, levopimaric acid,

all of the hydroxyl groups of the alcohol has been esterified by a resin acid selected from the group consisting of d-pimaric acid, levopimaric acid,

abietic acids and Palkin acids, and other hydroxyl roups have been acetalized in pairs by an aldehyde selected from the group consisting of aliphatic aldehydes having not more than 8 carbon atoms in the molecule and benzaldehyde.

8. A composition which comprises a copolymer of 1,3-butadiene and acrylonitrile and incorporated therewith as a tack-imparting softener, an ester-acetal of a polyhydric alcohol selected from the group consisting of glycerol, pentaerythritol and polypentaerythritols, in which at least one but not all of the hydroxyl groups of the alcohol has been esterified by a resin acid selected from the group consisting of d-pimaric acid, levopimaric acid, abietic acids and Palkin acids, and other hydroxyl groups have been acetalized in pairs by an aldehyde selected from the and benzaldehyde.

group consisting of aliphatic aldehydes having not more than 8 carbon atoms in the molecule HARRY BURRELL. ROBERT H. EARTH.

No references cited. 

1. A COMPOSITION COMPRISING INITIALLY A SYNTHETIC RUBBER PREPARED BY THE COPOLYMERIZATION OF A 1,3-BUTADIENE HYDROCARBON AND A MEMBER SELECTED FROM THE GROUP CONSISTING OF STYRENE AND ACRYLONITRILE AND, AS A TACK-IMPARTING SOFTENER THEREFOR, AN ESTER-ACETAL OF A POLYHYDRIC ALCOHOL SELECTED FROM THE GROUP CONSISTING OF GLYCEROL, PENTAERYTHRITOL AND POLYPENTAERYTHRITOLS, IN WHICH AT LEAST ONE BUT NOT ALL OF THE HYDROXYL GROUPS OF THE ALCOHOL HAS BEEN ESTERIFIED BY A RESIN ACID SELECTED FROM TEH GROUP CONSISTING OF D-PIMARIC ACID, LEVOPIMARIC, ABIETIC ACIDS AND PALKIN ACIDS, AND THE REMAINING HYDROXYL GROUPS HAVE BEEN ACETALIZED IN PAIRS BY AN ALDEHYDE SELECTED FROM THE GROUP CONSISTING OF ALIPHATIC ALDEHYDES HAVING NOT MORE THAN 8 CARBON ATOMS IN THE MOLECULE AND BENZALDEHYDE. 